This application is based upon and claims the benefit of Japanese Patent Applications No. 10-214495 filed on Jul. 29, 1998, No. 10-217725 filed on Jul. 31, 1998, and No. 10-276083 filed on Sep. 29, 1998, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a method of manufacturing a semiconductor device having a thin film resistor, and particularly to a method of etching a metallic thin film on the thin film resistor.
2. Description of the Related Art
A conventional method of manufacturing a CrSi resistor device including a CrSi resistor and a TiW barrier metal will be explained referring to FIGS. 1A to 1D. First, as shown in FIG. 1A, a CrSi film is deposited on a silicon substrate 101 through a silicon oxide film 102 interposed therebetween, and is patterned in to a shape of a CrSi resistor 103. Then, as shown in FIG. 1B, a TiW film 104 as barrier metal is deposited to cover the CrSi resistor 103, and an Al film 105 is deposited as electrodes. After that, as shown in FIG. 1C, the Al film 105 is patterned by etching using a photo-resist 106 as a mask. As shown in FIG., 1D, an unnecessary part of the TiW film 104 is further removed by wet etching using the photo-resist 106 as a mask again.
FIG. 2 is an enlarged view showing a portion around the CrSi resistor 103 formed by the conventional method described above. As shown in the figure, the conventional method is accompanied by Al over-hanging such that the Al film 105 is inversely tapered by the wet etching for the TiW film 104, and TiW under-cut such that the etching of the TiW film 104 progresses under the Al film 105. As a result, the Al film 105 and the TiW film 104 form an inversely tapered cross-sectional shape as a whole. The inversely tapered cross-sectional shape adversely affect a shape of an intermediate insualtion film which covers the CrSi resistor device, and further affects not only a shape of a wiring pattern formed on the insulation film but also a shape of a protective film for covering the wiring pattern. This may result in breakage of the wiring pattern and cracks in the protective film.
Further, as shown in FIG. 3, when the under-cut amount of the TiW film 104 is large, it becomes difficult for an intermediate insulation film 108 to fill the under-cut portion. This results in deterioration of step-coverage, and allows invasion of water or the like. As a rsult, the reliability of the device is lowered. Incidetnally, FIG. 3 omits the over-hanging porption of the Al film 105.
The present invention has been made in view of the above problems. An object of the present invention is to prevent under-cut of a barrier metal from being produced by etching of the barrier metal. Another object of the present invention is to prevent over-hanging of a conductive film from being produced by etching of the barrier metal. Still another object of the present invention is to provide a semiconductor device including a thin film resistor with high reliability.
According to a first aspect of the present invention, a first opening is formed in a conductive film to expose a metallic film (barrier metal) that is formed on a thin film resistor, and then a mask is formed on the conductive film with a second opening having an opening area smaller than that of the first opening and open in the first opening to expose the metallic film therefrom. Then, the metallic film is etched through the second opening. Accordingly, because the metallic film is etched from an inner portion more than the opening end of the first opening, the metallic film underlying the conductive film is hardly etched, thereby preventing under-cut of the metallic film.
According to a second aspect of the present invention, after a first part of a metallic film is dry-etched through an opening of a conductive film, a second part of the metallic film directly contacting a thin film resistor is wet-etched. Because a side etching amount produced by dry-etching is smaller than that produced by wet-etching, a variation in the side etching amount produced during the etching of the metallic film is decreased. As a result, a variation in a contact width between the metallic film and the thin film resistor is decreased, thereby achieving high reliability of a semiconductor device.
According to a third aspect of the present invention, a conductive film is formed on a metallic film to have a thickness equal to or less than 300 nm, and the conductive film is patterned to have an upper surface area, a ratio of which relative to an upper surface area of a thin film resistor is equal to or more than 0.02. Then, the metallic film is etched through an opening of the conductive film. Accordingly, a variation in an etching amount produced due to a battery effect between the conductive film and the metallic film is decreased to prevent over-hanging of the conductive film and under-cut of the metallic film.
According to a fourth aspect of the present invention, after a surface portion of a metallic film is oxidized to form a surface oxide layer, a conductive film is formed on the surface oxide layer. Then, the surface oxide layer and the metallic film are wet-etched through an opening of the conductive film. In this case, a potential difference produced between the metallic film and the conductive film at the wet-etching step is decreased by the surface oxide layer. As a result, the conductive film is prevented from being etched during the wet-etching step, thereby preventing the overhanging of the conductive film.